Advanced aircraft and aerospace systems demand light weight structures which are dependent upon the availability and effective utilization of superior structural materials. The material requirements are not only for superior mechanical properties, but it is also necessary that the materials possess a high degree of thermal oxidative stability.
The most attractive class of nonmetallic polymeric materials fulfilling both the superior mechanical and thermal stability property requirements are the aromatic heterocyclic polymers. Unfortunately, the most thermally stable systems in this class of materials are formed by condensation reactions with the evolution of by-products. In the fabrication of reinforced composite structure, the volatile by-products, which are evolved, form voids in the structures. As a result of the voids, the structures are greatly weakened, thereby rendering them unsatisfactory for use in aircraft and aerospace systems. Thus, there is a need for a heterocyclic oligomeric material possessing all the required fabrication criteria that can be converted to a thermally stable, high molecular weight polymer by a non-volatile addition reaction.
It is an object of this invention, therefore, to provide quinoxaline oligomers which propagate and cure by addition reactions to form high molecular weight, thermally stable compositions.
Another object of the invention is to provide ethynyl end-capped quinoxaline oligomers.
A further object of the invention is to provide a process for synthesizing ethynyl end-capped quinoxaline oligomers.
Still another object of the invention is to provide quinoxaline oligomers which are soluble in low boiling organic solvents, exhibit low softening points, and cure in a short period of time.
A still furher object of the invention is to provide quinoxaline oligomers which can be readily cured in a rapid manner to high molecular weight polymers having superior physical properties and possessing a high degree of thermal oxidative stability.
Other objects and advantages of the invention will become apparent to those skilled in the art upon consideration of the ensuing disclosure and the drawing which is a graph demonstrating the thermal oxidative stability of a cured quinoxaline oligomer of this invention.